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Exponential VCA... some math
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Exponential VCA... some math
CLee
...very little math actually, but I'm checking my math for an exponential VCA

IF: The VCA has an 80db dynamic range and a 0-5v CV with 5v being 0db/unity gain. And a 10v p/p signal at the input.

These would be the p/p readings for the output at various CV INs
5v CV = 10v out, 0db
4v CV = 1.5v out, -16.2db
3v CV = 0.24v out, -32.4db
2v CV = 0.037v out, -48.6db
1v CV = 0.0057v out, -64.8db
0v CV = 0.001v out, -80db

All of my VCAs have been linear, so I guess I'm looking for confirmation that these would be correct readings and this is expected behavior.
guest
close, but it should be -16dB steps, and not -16.2dB steps. the PP voltages would need to be recalculated as well.
CLee
guest wrote:
close, but it should be -16dB steps, and not -16.2dB steps. the PP voltages would need to be recalculated as well.


Thanks guest. I was rounding when I said 80db.

V2164 is 33mv/db and my 0 to 5v CV is scaled to 2.7v giving me 2.7/.033=81.8db. If I divide the 81.8db by 5v I actually get 16.8db/volt (not the 16.2 I stated). I think I rounded to 81 for some reason and then divided to get db/volt.

But in general I was hoping for some confirmation on the basic response. I'm not used to exponential VCAs and was a little surprised at how much change happens within a single volt.
guest
yes, the general format is correct. and it should change a lot at the beginning.
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